2001ApJ...563..919H

Radio data obtained over more than 13 years of monitoring give detailed spectra of the youngest known protostars in the young star formation region Cepheus A. Two sources, namely HW 2 and HW 3(d), increase in flux density from 15 to 43 GHz, as previously known. The data confirm that HW 2 appears to be thermal, producing two ionized jets, and these jets show an averaged separation speed of 95 km.s^–1, in comparison with the difference in the red and blue HCO⁺ outflow velocities of 54 km.s^–1. The jets appear to be acting as pistons to produce the molecular outflows. HW 3(c) has time-dependent spectra which decrease between 1.4 and 4.9 GHz, rise to a peak near to 15 GHz, and then fall rapidly to 43.3 GHz. The low-frequency emission appears to be synchrotron radiation from a jet, and the high-frequency emission indicates gyrosynchrotron radiation. HW 3(d) is somewhat similar at the lower frequencies but at the higher frequencies is doubly peaked. One component has a steeply rising spectrum, as for HW 2. HW 3(d) is similar to the double source of L1551 NW but is unlikely to be a double protostar. The data from the whole region, including previous analyses, show time-dependent events that are less than 1000 yr old. The events consist of variations in both flux density and spectra and involve high-energy electrons. These time-dependent variations, together with measured proper motions, indicate that extremely energetic events occur in protostars before they reach the Class 0 stage and could play an important part in dispersing the surrounding gas. Caution must be observed when interpreting processes in protostar-forming regions if they are observed only in the snapshot mode.